I need to replicate in my local openldap server all the entries in a
given subtree of a
remote openldap server, but the two DITs differ.
That means I'd like to replicate all entries under
"dc=people,dc=A,dc=it" (remote server)
to "dc=employees,dc=B,dc=it" (local server).

Can syncrepl do that? Or is there another way to obtain this?

Some setup with slapo-rwm comes to mind.

so I believe this means syncrepl can't map a DIT fragment onto a DIT fragment
with a different suffix.

Yes. But since syncrepl works with search requests one could try to map
things with slapo-rwm. But note that it can get tricky. I didn't try
that my self.

Maybe it would be easier to consolidate name spaces. You could also
replicate the original name space and then map search requests at your
local server to the name spaces wanted.